KR100516573B1 - Process for producing hexafluoroethane and use thereof - Google Patents

Abstract

An object of the present invention is to provide a profitable method for producing CF ₃ CF ₃ using CF ₃ CHF ₂ containing a compound having a chlorine atom in its molecule and its use.

In the process of the present invention, by reacting a mixed gas containing CF ₃ CHF ₂ and a compound having a chlorine atom in the molecule with hydrogen fluoride in the presence of a fluorination catalyst, the main impurity CClF ₂ CF ₃ is converted to CF ₃ CF ₃ , CF ₃ CF ₃ CHF ₂ containing the CF ₃ is reacted with a fluorine gas on the bus in the presence of a diluent gas.

Description

Hexafluoroethane manufacturing method and its use {PROCESS FOR PRODUCING HEXAFLUOROETHANE AND USE THEREOF}

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The present invention is a step of fluorinating a compound having a chlorine atom by reacting a gas mixture containing pentafluoroethane and a compound having a chlorine atom with gaseous hydrogen fluoride in the presence of a fluorinated bulk catalyst obtained by adding indium to chromium oxide. And reacting a gas mixture containing pentafluoroethane and the fluorinated compound with fluorine gas in the gas phase in the presence of diluent gas and a use thereof.

Pentafluoroethane (hereinafter referred to as "CF ₃ CHF ₂ ") is used, for example, as a low temperature refrigerant or as starting material for the preparation of hexafluoroethane (hereinafter referred to as "CF ₃ CF ₃ ").

For the production of CF ₃ CHF ₂ , for example, the following methods are known to date.

(1) A method of fluorinating ethylene perchlorate (CCl ₂ = CCl ₂ ) or its fluoride with hydrogen fluoride (JP-A-597724 (JP-A here means Japanese Patent Laid-Open), JP-A- 6-506221, JP-A-7-76534, JP-A-7-118182, JP-A-8-268932 and JP-A-9-511515),

(2) a method for carrying out the hydrogenolysis of chloropentafluoroethane (CClF ₂ CF ₃ ), and

(3) A method of reacting halogen-containing ethylene with fluorine gas (JP-A-1-38034).

When using these methods for the production of CF ₃ CHF ₂ , the target CF ₃ CHF ₂ contains compounds having chlorine atoms in the molecule as major impurities. Compounds having chlorine atoms in a molecule include compounds having one carbon atom in a molecule such as chloromethane, chlorodifluoromethane and chlorotrifluoromethane, chloropentafluoroethane, dichlorotetrafluoroethane and chlorotetrafluoro And unsaturated compounds such as chlorotrifluoroethylene and compounds having two carbon atoms in the molecule such as ethane and chlorotrifluoroethane.

In the case of producing CF ₃ CF ₃ by a direct fluorination reaction in which fluorine gas (F ₂ ) and CF ₃ CHF ₂ are reacted, if CF ₃ CHF ₂ contains a compound having a chlorine atom in the molecule, fluorine gas The reaction with chlorine, hydrogen chloride, chlorine fluoride or different kinds of chlorofluorocarbons is produced. Even when hydrofluorocarbons (HFCs) or perfluorocarbons (PFCs) are contained in CF ₃ CHF ₂ , no particular problems arise, for example chloromethane (CH ₃ Cl) or chlorodifluoromethane (CHClF). ₂ ) reacts with fluorine gas to produce chlorotrifluoromethane (CClF ₃ ). Objective CF _{3 Since} CF ₃ and chlorotrifluoromethane form an azeotrope, CClF ₃ is difficult to remove even if distillation, adsorption or the like is carried out for purification. Therefore, CF ₃ CF case be reacted with fluorine gas CF ₃ CHF ₂ to ₃ produced, must be reduced so that the amount of the compound having a chlorine atom in the molecule contained in the CF ₃ CHF _2.

According to the conventional method for preparing CF ₃ CHF ₂ , the total amount of the compound having chlorine atoms in the molecule is sometimes 1 vol%. Hence, CF ₃ CHF remove the these compounds contained in the _2, one repeats the distillation operation in order to increase the purity of the CF ₃ CHF _2, which increases the distillation costs, is causing distillation loss, profitability is poor, the molecule Some compounds having chlorine atoms in them have problems that are difficult to form azeotrope or azeotrope mixture with CF ₃ CHF ₂ and remove by distillation alone. In particular, chloropentafluoroethane (hereinafter referred to as "CClF ₂ CF ₃ ") is generally contained in CF ₃ CHF _{2 at} concentrations of several thousand ppm or more, but an azeotrope is formed by CF ₃ CHF ₂ and CClF ₂ CF ₃ Therefore, it is difficult to separate by distillation which is a commonly used separation and purification method.

Several methods have been proposed for separating CClF ₂ CF ₃ contained in CF ₃ CHF ₂ . for example,

(1) A method of extractive distillation by adding a third component to a mixture of CF ₃ CHF ₂ and CClF ₂ CF ₃ (JP-A-6-510980, JP-A-7-133240, JP-A-7- 258123, JP-A-8-3082, JP-A-8-143486 and JP-A-10-513190),

(2) A method for removing CClF ₂ CF ₃ contained in CF ₃ CHF ₂ using an adsorbent (see JP-A-6-92879 and JP-W-8-508479 ("JP-W" is referred to here as International Patent Publication). ) And

(3) under the presence of CF ₃ CHF ₂ CClF ₂ CF ₃ a method for switching to the _{CF 3 CHF 2 (JP-A} -7-509238, JP-A-8-40949, JP-A-8 contained in the hydrogenation catalyst -301801 and JP-A-10-87525).

However, in these methods, the method of (1) requires the step of recovering the third component from the mixture of CClF ₂ CF ₃ and the third component, and the method of (2) requires regenerating the adsorbent. The method of (3) has a problem in that the catalyst life is shortened due to the generated hydrogen chloride.

The present invention has been made in view of such a situation, and an object of the present invention is to produce CF ₃ CF ₃ which is used as an etching or cleaning gas in a method of manufacturing a semiconductor device, in which CF ₃ CHF ₂ and a chlorine atom in a molecule It is to provide a method for producing a good yield of CF ₃ CF ₃ using a gas mixture containing a compound containing and to provide its use.

In order to solve the above problems, as a result of extensive investigation, the present inventors have found that in the method for preparing CF ₃ CF ₃ , a gas mixture containing CF ₃ CHF ₂ and a compound having a chlorine atom in its molecule as an impurity is contained in chromium oxide. The reaction gas is reacted with hydrogen fluoride in the presence of a fluorinated bulk catalyst obtained by addition of indium to convert CClF ₂ CF ₃ contained in the gas mixture to CF ₃ CF ₃ , followed by CF ₃ CHF ₂ and CF ₃ CF ₃ It has been found that the above problems can be solved by performing the direct fluorination reaction by reacting the mixture with gaseous fluorine gas in the presence of diluent gas. The present invention has been accomplished based on this finding. The present invention provides a method for producing CF ₃ CF ₃ and its use as described in (1) to (19) below.

[One]. The method for preparing hexafluoroethane includes the following two steps.

(1) fluorinating a compound containing chlorine atoms by reacting a gas mixture containing pentafluoroethane and a compound containing chlorine atoms with gaseous hydrogen fluoride in the presence of a fluorinated bulk catalyst obtained by adding indium to chromium oxide. ; And

(2) reacting a gas mixture containing pentafluoroethane and the fluorinated compound obtained in step (1) with fluorine gas in the gas phase in the presence of diluent gas.

[2]. In the method for producing hexafluoroethane according to [1], the compound having a chlorine atom includes chloromethane, chlorotrifluoromethane, chloropentafluoroethane, dichlorotetrafluoroethane, chlorotetrafluoroethane, At least one compound selected from the group consisting of chlorotrifluoroethane and chlorotrifluoroethylene.

[3]. In the method for producing hexafluoroethane according to [1] or [2], the total amount of the compound having a chlorine atom contained in the gas mixture of step (1) is 1 vol% or less.

[4]. In the method for producing hexafluoroethane according to [1] or [2], the total amount of the compound having chlorine atoms contained in the gas mixture of step (1) is 0.5% by volume or less.

[5]. In the method for producing hexafluoroethane according to [1] or [2], the fluorination catalyst of step (1) is a bulk catalyst obtained by adding indium to chromium oxide.

[6]. In the method for producing hexafluoroethane according to [1] or [2], the temperature during the reaction with hydrogen fluoride in the presence of the fluorination catalyst of step (1) is in the range of 150 to 480 ° C.

[7]. In the method for producing hexafluoroethane according to [1] or [2], the molar ratio of hydrogen fluoride / organic matter contained in the gas mixture of step (1) is in the range of 0.5 to 5.

[8]. In the method for producing hexafluoroethane as described in [1] or [2], the step of removing the acid content contained in the produced hydrogen chloride is performed before step (2).

[9]. The process for producing hexafluoroethane according to [1] or [2], wherein the step of separating chlorotetrafluoroethane and / or chlorotrifluoroethane and the separated chlorotetrafluoroethane and / or chlorotrifluoro Restoring the ethane in step (1) is performed before step (2).

[10]. In the method for producing hexafluoroethane according to [1] or [2], the total amount of the compound having chlorine atoms contained in the gas mixture of step (2) is 0.02% by volume or less.

[11]. In the method for producing hexafluoroethane as described in [1] or [2], the fluorinated compound contained in the gas mixture of step (2) is mainly composed of hexafluoroethane.

[12]. In the method for producing hexafluoroethane according to [1] or [2], the diluent gas of step (2) is selected from the group consisting of tetrafluoromethane, hexafluoroethane, octafluoropropane and hydrogen fluoride. It is a gas containing at least one selected.

[13]. In the method for producing hexafluoroethane according to [1] or [2], the diluent gas of step (2) is a gas rich in hydrogen fluoride.

[14]. In the method for producing hexafluoroethane according to [1] or [2], the temperature during the reaction of the gas mixture containing fluorinated compound of step (2) with fluorine gas is in the range of 250 to 500 ° C. .

[15]. In the method for producing hexafluoroethane as described in [1] or [2], the temperature during the reaction of the gas mixture containing the fluorinated compound of step (2) with fluorine gas is in the range of 350 to 450 ° C. .

[16]. It is a hexafluoroethane product prepared by the method described in [1] above and containing hexafluoroethane having a purity of 99.9997% by volume or more.

[17]. In the hexafluoroethane product described in [16], the content of the compound having a chlorine atom is 1 ppm by volume or less, and the content of pentafluoroethane is 1 ppm by volume or less.

[18]. The etching gas contains the hexafluoroethane product described in [16] or [17].

[19]. The washing gas contains the hexafluoroethane product described in [16] or [17].

In summary, the present invention "CF ₃ CHF stage a gas mixture containing the ₂ and a compound having a chlorine atom is reacted with gaseous hydrogen fluoride in the presence of a fluorination catalyst which is a compound having the chlorine atoms fluorinated, and CF ₃ CF ₃ CF ₃ method comprising the step of reacting a gas mixture containing CHF ₂ and the fluorinated compound obtained in the step with a gaseous fluorine gas in the presence of a diluent gas, "CF _{3 having a} purity of 99.9997% by volume or more CF ₃ CF ₃ product containing CF ₃ ”,“ etching gas containing CF ₃ CF ₃ product ”and“ wash gas containing CF ₃ CF ₃ product ”.

The preparation method of CF ₃ CF ₃ and its use according to the invention are described below.

As mentioned above, CF ₃ CHF ₂ for use in the present invention is generally produced by fluorinating perchlorate ethylene (CCl ₂ = CCl ₂ ) or its fluoride with hydrogen fluoride, and CF ₃ CHF ₂ is chloromethane, chloro A compound having a chlorine atom derived from starting materials such as difluoromethane, chlorotrifluoromethane, chloropentafluoroethane, dichlorotetrafluoroethane, chlorotetrafluoroethane and chlorotrifluoroethane. In order to purify CF ₃ CHF ₂ containing these compounds with high purity, known methods by distillation operation are employed, but these methods are used for separation because the compound and CF ₃ CHF ₂ form an azeotrope or azeotrope. Purification is very difficult, and because the number of stages or distillation column of the distillation column has to be increased, there is a problem that is not economical because the device or energy cost is increased.

In the present invention, a compound having a chlorine atom contained in CF ₃ CHF ₂ as an impurity is converted to hydrofluorocarbon (HFC) or perfluorocarbon (PFC) by fluorination with hydrogen fluoride at elevated temperature in the presence of a fluorination catalyst. . For example, in the fluorination of CClF ₂ CF ₃ or chlorotetrafluoroethane contained as impurities in CF ₃ CHF ₂ with hydrogen fluoride, the reaction is represented by the following general formula (1) or (2).

CF ₃ CClF ₂ + HF → CF ₃ CF ₃ + HCl (1)

CF ₃ CHClF + HF → CF ₃ CHF ₂ + HCl (2)

The product is HFC or PFC free of chlorine atoms and hydrogen chloride is produced as a by-product.

In the present application, a mixed gas containing CF ₃ CHF ₂ and a compound having a chlorine atom is sometimes referred to as a “starting gas mixture”.

In this fluorination reaction, compounds converting to HFC or PFC are chloromethane, chlorodifluoromethane, chlorotrifluoromethane, chloropentafluoroethane, dichlorotetrafluoroethane, chlorotetrafluoroethane and chlorotrifluoro It's ethane. These compounds are generally contained in CF ₃ CHF ₂ in total amounts of several thousand ppm or more. When the starting gas mixture containing these compounds reacts with fluorine gas, the methane compounds convert to CClF ₃ and the ethane compounds convert to CClF ₂ CF ₃ , so that CF ₃ CF ₃ obtained after the reaction is a major impurity. ₃ and CClF ₂ CF ₃ .

CClF ₂ CF ₃ hardly reacts with fluorine gas at low temperatures. However, according to the investigation by the inventors, for example, the amount of CClF ₃ produced by decomposition of CClF ₂ CF ₃ at a reaction temperature of 400 ° C. is 1 ppm when the concentration of CClF ₂ CF ₃ contained in the starting gas mixture is about 800 ppm or less. When the concentration of CClF ₂ CF ₃ is less than about 2,000 ppm, about 2 ppm of CClF ₃ is produced. CClF ₃ forms an azeotrope with CF ₃ CF ₃ , so even if the concentration is low, it is difficult to remove the compound by distillation, adsorption, or the like to purify the compound. Therefore, the CClF ₃ compound produced by reaction with fluorine gas should be removed from the starting material CF ₃ CHF _2, and the content of CClF ₂ CF ₃ should be reduced as low as possible.

The total amount of the compound having chlorine atoms contained in the starting gas mixture for use in the present invention is preferably 1 vol% or less, more preferably 0.5 vol% or less, and even more preferably 0.3 vol% or less. If the concentration of the compound having chlorine atoms is more than 1% by volume, the reaction should be carried out at a high temperature, the lifetime of the fluorination catalyst is disadvantageously shortened, and the side reactions occur simultaneously, and the productivity decreases.

The fluorination catalyst contains at least one element selected from the group consisting of chromium, nickel, zinc, indium and gallium, and may be a known catalyst such as a supported catalyst or a bulk catalyst.

In the case of a supported catalyst, the carrier is preferably alumina and / or partially fluorinated alumina, and the support rate is preferably 30% by weight or less. In the case of bulk catalysts, in particular, it is preferable to contain chromium as the main component, and the atomic ratio of nickel, zinc, indium and / or gallium: chromium is 0.01: 0.6. In this invention, the bulk catalyst obtained by adding indium to the oxide of chromium is the most preferable.

In the fluorination step of the compound having a chlorine atom, the reaction temperature is preferably 150 to 480 ° C. If the reaction temperature exceeds 480 ° C., for example, the reaction has an adverse effect that the catalyst deteriorates or a side reaction occurs, which is undesirable. Although it depends on the change in the concentration of the compound contained in the starting gas mixture, the reaction temperature is preferably selectable according to the type of compound. For example, in the reaction of CClF ₂ CF ₃ shown in the general formula (1), the reaction temperature is preferably 400 ° C or higher, and in the reaction of CF ₃ CHClF shown in the general formula (2), the reaction temperature is preferably 300 ° C or higher.

In the case of reaction of hydrogen fluoride and chlorodifluoromethane (CHClF ₂ ), it becomes reaction shown by following General formula (3).

CHClF ₂ + HF → CHF ₃ + HCl (3)

In this reaction, the reaction temperature is preferably 150 ° C. or higher, and when the reaction temperature exceeds 400 ° C., the reverse reaction proceeds disadvantageously.

In the fluorination step of a compound having a chlorine atom, the reaction temperature sometimes changes depending on the kind of the following compound. Therefore, when a large number of compounds are contained, each having a different optimum reaction temperature range or the concentration of each compound is high, it is preferable to use two or more reactors, but one reactor is generally sufficient.

The amount of HF to be used is preferably 0.5 to 5, preferably 0.5 to 2, depending on the molar ratio of the starting gas mixture containing CF ₃ CHF ₂ (HF / organic) to the organics. If the molar ratio is lower than 0.5, the reaction is difficult to proceed, whereas if it exceeds 5, a large reactor is required and this is not advantageous.

In addition, the reaction pressure in the fluorination step of the compound having a chlorine atom is preferably 1.5 MPa at atmospheric pressure. If it exceeds 1.5 MPa, the devices are disadvantageous due to the need for pressure resistance and the like.

In the present invention, the reaction with hydrogen fluoride is carried out in the presence of a fluorination catalyst using the following reaction conditions, and then hydrogen chloride as a by-product and chlorine-free impurities mainly containing CF ₃ CHF ₂ , HFC or PFC are contained in the reaction product. . In the case of CF ₃ CHF ₂ , when the reaction temperature is high, the side reaction with hydrogen chloride proceeds further as shown in the following general formula (4).

CF ₃ CHF ₂ + HCl → CF ₃ CHClF + HF (4)

In the case of containing 1,1,1,2-tetrafluoroethane, the side reaction with hydrogen chloride proceeds further as shown by the following general formula (5).

CF ₃ CH ₂ F + HCl → CF ₃ CH ₂ Cl + HF (5)

Therefore, after the fluorination of step (1), the acid content of the generated hydrogen chloride is preferably removed.

The acid content is removed to remove unreacted hydrogen fluoride (excess hydrogen fluoride) and by-product hydrogen chloride. Hydrogen fluoride does not cause a direct adverse effect on the fluorination reaction step, but hydrogen chloride is preferably removed because it sometimes leads to adverse effects such as the production of chlorine-containing compounds or chlorine fluoride as shown in general formula (4) or (5). . Removing the acid content is carried out before the direct fluorination step. Examples of acid removal methods include:

(1) in the case of containing a large amount of unreacted hydrogen fluoride, introducing a discharge containing an acid content into the distillation column, extracting hydrogen chloride from the top of the column, and extracting organic matter and hydrogen fluoride from the bottom;

(2) contacting the produced hydrogen chloride and unreacted hydrogen fluoride with a purifying agent, and

(3) washing the acid content with water or alkaline water

Can be mentioned.

       In the present invention, the method of removing the acid content is not particularly limited, but for example, the method of (3) can be used. The alkali used therein may be an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or the like. The absorbed hydrogen fluoride can be recovered and reused, and the gas passed through the cleaning liquid is dehydrated using a dehydrating agent such as zeolite.

Gases containing mainly CF ₃ CHF ₂ , which have passed through the acid content removal step, often contain HCFCs or CFCs as impurities, which are not fully fluorinated by reaction with hydrogen fluoride, in which case HCFCs or CFCs are directly fluorinated It is preferably removed by distillation before the step.

The main compounds that can be contained in CF ₃ CHF ₂ and CF ₃ CHF ₂ are shown in Table 1 with their respective boiling points.

Compound name constitutional formula Boiling Point (℃) Tetrafluoromethane CF ₄ -128 Trifluoromethane CHF ₃ -84 Hexafluoroethane CF ₃ CF ₃ -78.1 Pentafluoroethane CF ₃ CHF ₂ -48.5 Chloropentafluoroethane CF ₃ CClF ₂ -38.7 2-chloro-1,1,1,2-tetrafluoroethane CF ₃ CHClF -12 2-chloro-1,1,1-trifluoroethane CF ₃ CH ₂ Cl 6.1

A gas mainly containing CF ₃ CHF ₂ is introduced into the distillation column, and then CF ₄ , CHF ₃ , CF ₃ CF ₃ , CF ₃ CHF ₂ and CClF ₂ CF ₃ as low boiling parts are extracted from the top of the distillation column, As the high boiling part, CF ₃ CHClF and CF ₃ CH ₂ Cl are extracted from the bottom. The high boiling part extracted from the column bottom circulates and reacts with hydrogen fluoride in step (1). Here, the total amount of the compound having chlorine atoms contained in the distilled material mainly containing CF ₃ CHF ₂ extracted from the column top is preferably 0.02% by volume or less. Distillates containing mainly CF ₃ CHF ₂ are used as starting materials in the direct fluorination reaction with fluorine gas.

Step (2) of the gas reaction mainly containing fluorine gas and CF ₃ CHF ₂ is described below.

Step (2) is carried out in the presence of diluent gas, and gases containing mainly CF ₃ CHF ₂ start at concentrations below the explosive range. In particular, the CF ₃ CHF ₂ concentration at the reactor inlet preferably begins below about 6 mol%. The diluent gas is a gas containing at least one selected from the group consisting of tetrafluoromethane, hexafluoroethane, octafluoropropane and hydrogen fluoride, and a diluent gas rich in hydrogen fluoride is preferable.

In the molar ratio of CF ₃ CHF ₂ (F ₂ / CF ₃ CHF ₂ ), the amount of fluorine gas used is preferably within the range of 0.5 to 2, and preferably from 0.9 to 1.3. The reaction temperature is in the range of 250 to 500 캜, preferably in the range of 350 to 450 캜. When the reaction temperature exceeds 500 ° C., the target CF ₃ CF ₃ is unfavorably cleaved to produce CF _{4 and} when CClF ₂ CF ₃ is contained as an impurity, CClF ₃ is disadvantageous due to cleavage of CClF ₂ CF ₃ . On the other hand, if lower than 250 ° C., the reaction proceeds slowly, which is undesirable.

The method of purifying the gas distilled from the reaction step of (2) is not particularly limited. The remainder of the unreacted fluorine gas can be removed, for example, by addition of trifluoromethane as HCF, and then the residue is separated and distilled, for example, into hydrogen fluoride and organic matter. The separated hydrogen fluoride is reused as a diluent gas in the direct fluorination reaction of step (2), but may be used as a starting material in the fluorination reaction of (1). The composition of the separated organic substance is very dependent on the diluent gas used for the reaction, and the organic substance obtained when using a gas containing a large amount of hydrogen fluoride or target gas CF ₃ CF ₃ contains CF ₃ CF ₃ as a main component. . In the case of using tetrafluoroethane or octafluoropropane as the diluent gas, the gas is purified again by performing distillation. In either case, high purity CF ₃ CF ₃ can be obtained by performing the distillation operation again in accordance with the composition ratio of the obtained organic matter.

In distillation for the purification of organics, although it may vary depending on the composition ratio, for example, as an inert gas and a low boiling part, CF ₄ is extracted from the top of the first column, and gases containing mainly CF ₃ CF ₃ are removed from the bottom. Extracted and introduced into a second distillation column. By then, trifluoroacetate as a portion, such as an inert gas and a low-cost methane is extracted from the top of the second distillation column, CF ₃ containing CF ₃ mainly gas is extracted from the column bottom, high purity CF ₃ CF ₃ are extracted from the top third distillation column Purification is carried out by introducing into. The gas containing CClF ₂ CF ₃ collected from the bottom in the third distillate will be circulated to the reaction step with hydrogen fluoride in (1).

Such pure CF ₃ CF ₃ hardly contains impurities and high purity CF ₃ CF ₃ can be obtained. Its purity is 99.9997% by volume or more, 1 ppm by volume or less of the compound having a chlorine atom, and 1 ppm by volume or less of pentafluoroethane contained as impurities.

CF ₃ CF _{3 having} a purity of 99.9997% by volume or more can be analyzed by gas chromatography (GC) or gas chromatography mass spectrometry (GC-MS) using TCD method, FID method (each method including pre-cutting method) or ECD method. Precision instruments such as) can be used.

The use of CF ₃ CF ₃ obtained by the production method of the present invention is described below.

High purity CF ₃ CF ₃ can be used as an etching gas in the etching step of the semiconductor device manufacturing method, it can also be used as a cleaning gas in the cleaning step of the semiconductor device manufacturing method.

In semiconductor device manufacturing methods such as LSI and TFT, a thin film or a thick film is formed by CVD, sputtering, or vapor deposition, and the film is etched to form a circuit pattern. The device for forming the thin film or the thick film is cleaned to remove unnecessary deposits that accumulate on the inner wall of the jig device, etc., because the unnecessary deposits sometimes need to be removed to cause the production of particles and to form a film of good quality. to be.

The etching method using CF ₃ CF ₃ can be carried out under various dry etching conditions such as plasma etching and microwave etching, and CF ₃ CF ₃ is inert such as helium, nitrogen and argon or HCl, O ₂ , H ₂ in an appropriate ratio. It can be mixed with gas and used.

(Example)

The invention is described in more detail by the following examples and comparative examples, but the invention is not limited to these examples.

Raw material example 1

Tetrachloroethylene (CCl ₂ = CCl ₂ ) in the presence of a fluorination catalyst is reacted with HF at a reaction pressure of 0.4 MPa, a reaction temperature of 300 ° C. and a molar ratio of HF / tetrachloroethylene of 4 (first reaction), and then the reaction. Was continued at a reaction pressure of 0.4 MPa, a reaction temperature of 330 ° C. and a molar ratio of HF / intermediate of 4 (CF ₃ CHCl ₂ + CF ₃ CHClF) (second reaction). After the reaction, acid content removal and distillation were carried out by a conventional method, and as a result of analyzing the distilled material by gas chromatography, crude CF ₃ CHF ₂ (CF ₃ CHF _{2 as} a raw material of the composition shown in Table 2). 1) was obtained.

compound Purity (% by volume) CF ₃ CHF ₂ 99.4513 CH ₃ Cl 0.0011 CHClF ₂ 0.0008 CHF ₃ 0.0224 CClF ₃ 0.0005 CF ₃ CClF ₂ 0.5216 CF ₃ CHClF 0.0008 CF ₃ CCl ₂ F 0.0009 CF ₃ CH ₂ Cl 0.0006

Raw material example 2

The raw material 1 of CF ₃ CHF ₂ obtained by the above method was distilled again by the conventional method, and the result of analysis of the distilled material by gas chromatography showed that crude CF ₃ CHF ₂ having the composition shown in Table 3 (raw material 2 of CF ₃ CHF ₂₎ . )

compound Purity (% by volume) CF ₃ CHF ₂ 99.8000 CHClF ₂ 0.0002 CHF ₃ 0.0038 CF ₃ CClF ₂ 0.1960

Catalyst Example 1

In a 10 L-volume vessel containing 0.6 L of pure water, a solution containing 452 g of Cr (NO ₃ ) ₃ · 9H ₂ O dissolved in 1.2 L of pure water, and 0.31 L of 28% aqueous ammonia solution, having a pH of 7.5 to 8.5 It was added dropwise over about 1 hour with stirring to adjust. The obtained hydroxide slurry was filtered, washed thoroughly with pure water, and then dried at 120 ° C. The solid thus obtained was ground, mixed with graphite, and then granulated with a tableting machine. The obtained particles were calcined at 400 ° C. for 4 hours in nitrogen to obtain a catalyst precursor. The catalyst precursor was charged to a reactor made by Inconel, followed by fluorination treatment (activation of the catalyst) under atmospheric pressure and HF atmosphere diluted with nitrogen at 350 ° C., followed by dilution with nitrogen in 100% HF. The catalyst was prepared by further treatment at 450 ° C. under HF atmosphere.

Catalyst Example 2

452 g of Cr (NO ₃ ) ₃ · 9H ₂ O and 42 g of In (NO ₃ ) ₃ · nH ₂ O (n is about 5) in a ₁₀ L-volume vessel containing 0.6 L of pure water. A solution and 0.31 L of an aqueous 28% ammonia solution were added dropwise over about 1 hour while stirring the flow rates of the two aqueous solutions to adjust the reaction solution having a pH of 7.5 to 8.5. The hydroxide slurry obtained was filtered, washed thoroughly with pure water and then dried at 120 ° C. for 12 hours. The solid thus obtained was ground and mixed with graphite and then granulated with a tableting machine. The obtained particles were calcined at 400 ° C. for 4 hours with nitrogen steam to obtain a catalyst precursor. The catalyst precursor was filled in a reactor made by Inconel, followed by fluorination treatment (activation of the catalyst), which is the same method as in Catalyst Example 1, to prepare a catalyst.

Example 1 Step (1)

150 ml of the catalyst prepared in [Catalyst Example 1] was charged into an Inconel manufactured 600-type reactor having an inner diameter of 1 inch and a length of 1 m, and the temperature was raised to 440 ° C while passing through nitrogen gas. Hydrogen fluoride was supplied thereto at 3.5 NL / hr, and then raw material 1 of CF ₃ CHF ₂ obtained in [Raw Material Example 1] was fed at 3.5 NL / hr. The supply of nitrogen gas was stopped and the reaction was started. After 2 hours, the exhaust gas was washed with an aqueous potassium hydroxide solution to remove the acid content, and then the gas composition was analyzed by gas chromatography to obtain a gas having the composition shown in Table 4.

compound Purity (% by volume) CF ₃ CHF ₂ 99.3273 CF ₄ 0.0113 CHF ₃ 0.0215 CF ₃ CF ₃ 0.6120 CF ₃ CClF ₂ 0.0156 CF ₃ CHClF 0.0112 CF ₃ CH ₂ Cl 0.0011

Example 2 Step (1)

The reaction and analysis were carried out under the same conditions as in Example 1, except that 150 ml of the catalyst prepared in Catalyst Example 2 was charged as the catalyst. The analysis results are shown in Table 5.

compound Purity (% by volume) CF ₃ CHF ₂ 99.2732 CF ₄ 0.0170 CHF ₃ 0.0212 CF ₃ CF ₃ 0.6720 CF ₃ CClF ₂ 0.0068 CF ₃ CHClF 0.0098 CF ₃ CH ₂ Cl 0.0015

As is apparent from the analysis results shown in Table 5, the conversion from CClF ₂ CF ₃ to CF ₃ CF ₃ was improved when using the fluorination catalyst obtained by adding indium to chromium.

Example 3 Step (1)

The reaction and analysis were carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 300 ° C. The analysis results are shown in Table 6.

compound Purity (% by volume) CF ₃ CHF ₂ 99.4314 CF ₄ 0.0023 CHF ₃ 0.0221 CF ₃ CF ₃ 0.0387 CF ₃ CClF ₂ 0.4829 CF ₃ CHClF 0.0014 CF ₃ CH ₂ Cl 0.0005

(Example 4) Step (1)

      The reaction and analysis were carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 500 ° C. The analysis results are shown in Table 7.

compound Purity (% by volume) CF ₃ CHF ₂ 99.1948 CF ₄ 0.1488 CHF ₃ 0.0168 CF ₃ CF ₃ 0.5880 CHClF ₂ 0.0069 CF ₃ CClF ₂ 0.0148 CF ₃ CHClF 0.0256 CF ₃ CCl ₂ F 0.0021 CF ₃ CH ₂ Cl 0.0022

Example 5 Step (1) + (2)

150 ml of the catalyst prepared in [Catalyst Example 2] was charged into an Inconel 600-type reactor having an inner diameter of 1 inch and a length of 2 m, and the temperature was raised to 430 ° C while passing nitrogen. Hydrogen fluoride was supplied thereto at 5.0 NL / hr, and raw material ₂ of CF ₃ CHF ₂ obtained in [Raw Material Example 2] was supplied at 8.0 NL / hr. Subsequently, the supply of nitrogen gas was stopped, and 2 hours after the start of the reaction, the exhaust gas was washed with an aqueous potassium hydroxide solution to remove acid content. As a result of analyzing the obtained gas composition by gas chromatography, the gas which has a composition shown in Table 8 was obtained.

compound Purity (% by volume) CF ₃ CHF ₂ 99.7922 CF ₄ 0.0018 CHF ₃ 0.0036 CF ₃ CF ₃ 0.1980 CF ₃ CClF ₂ 0.0008 CF ₃ CHClF 0.0036

After removing the acid content, the gas having the composition shown in Table 8 was collected under cooling and the distillate was purified according to the conventional method. The gas obtained after purification was analyzed and the results are shown in Table 9.

compound Purity (% by volume) CF ₃ CHF ₂ 99.7950 CF ₄ 0.0019 CHF ₃ 0.0035 CF ₃ CF ₃ 0.1988 CF ₃ CClF ₂ 0.0008

As apparent from the analytical results shown in Table 9, most of the chlorotetrafluoroethane can be removed by performing distillation.

After purification by distillation obtained above, direct fluorination reaction with fluorine gas was performed using a gas mainly containing CF ₃ CHF ₂ .

Inconel's 600-type reactor with an inner diameter of 20.6 mm Φ and a length of 500 mm (heated by a heater; the reactor was passivated with fluorine gas at a temperature of 500 ° C.) was nitrogen gas at 30NL / hr. It heated to the temperature of 420 degreeC, passing it.

Then, hydrogen fluoride was supplied at 50 NL / hr, and a gas mainly containing CF ₃ CHF ₂ was supplied at 3.5 NL / hr into one gas stream branched from the diluent gas. The reaction was then carried out by supplying fluorine gas similarly at 3.85 NL / hr into another gas stream branched from the diluent gas. After 3 hours, the reaction product gas was washed with an aqueous potassium hydroxide solution and an aqueous potassium iodine solution to remove hydrogen fluoride and unreacted fluorine gas. The gas composition was then analyzed by gas chromatography. The analysis results are shown in Table 10.

compound Purity (% by volume) CF ₃ CHF ₂ 0.0001 CF ₄ 0.0456 CF ₃ CF ₃ 99.9536 CF ₃ CClF ₂ 0.0007

After acid content removal the gas was collected under cooling and purified by distillation. The gas after purification was analyzed by gas chromatography using TCD method, FID method, ECD method and GC-MS method, and the analysis results are shown in Table 11.

compound Purity (% by volume) CF ₃ CHF ₂ 0.9 volume ppm CF ₄ <0.4 ppm by volume SF ₆ <0.4 ppm by volume CF ₃ CClF ₂ <0.1 ppm by volume CF ₃ CF ₃ 99.9998% by volume

As apparent from the analytical results shown in Table 11, CF ₃ CF ₃ after purification contained almost no other impurities, so high purity CF ₃ CF ₃ was obtained, and its purity was 99.9997% by volume or more.

(Comparative Example 1)

Inconel's 600-type reactor with an inner diameter of 20.6 mm Φ and a length of 500 mm (heated by a heater; the reactor was passivated with fluorine gas at a temperature of 500 ° C.) was passed through nitrogen gas at 30 NL / hr. It was heated to a temperature of 420 ℃ while.

Then, hydrogen fluoride was supplied at 50 NL / hr, and raw material 1 of CF ₃ CHF ₂ obtained in [Raw Material Example 1] was supplied at 3.5 NL / hr into one gas stream branched from the diluent gas. The reaction was then carried out by feeding fluorine gas similarly at 3.85 NL / hr into another gas stream branched from the diluent gas. After 3 hours, the reaction product gas was washed with an aqueous potassium hydroxide solution and an aqueous potassium iodine solution to remove hydrogen fluoride and unreacted fluorine gas. The gas composition was then analyzed by gas chromatography. The analysis results are shown in Table 12.

compound Purity (% by volume) CF ₃ CHF ₂ 0.0003 CF ₄ 0.0568 CClF ₃ 0.0036 CF ₃ CF ₃ 99.4160 CF ₃ CClF ₂ 0.5233

As is clear from the analytical results shown in Table 12, CF ₃ CHF ₂ containing a compound having a chlorine atom in its molecule as an impurity produced CClF ₃ (chlorotrifluoromethane), a substance that was difficult to separate when reacted with fluorine gas. do.

Then, after removal of the acid content, the gas with the composition shown in Table 12 was collected under cooling and purified by distillation. The gas obtained after purification was analyzed and the results are shown in Table 13.

compound Purity (% by volume) CF ₃ CHF ₂ 0.0003 CF ₄ <0.0001 CClF ₃ 0.0036 CF ₃ CF ₃ 99.9959 CF ₃ CClF ₂ <0.0001

As is clear from the analytical results shown in Table 13, CClF ₃ is a difficult compound to separate.

Above as using a compound that holds the starting gas mixture, and chlorine gas containing CF ₃ CHF _2, and can produce high purity CF ₃ CF _3, according to the present invention, the resulting high purity CF ₃ CF ₃ A semiconductor device manufacturing process It can be used as an etching gas or a washing gas in the.

Claims (19)

(1) reacting a gas mixture containing pentafluoroethane and a compound having a chlorine atom with gaseous hydrogen fluoride in the presence of a bulk fluorination catalyst obtained by adding indium to chromium oxide to fluorinate the compound having a chlorine atom; step; And (2) a method for producing hexafluoroethane, comprising reacting a gas mixture containing pentafluoroethane and the fluorinated compound obtained in step (1) with fluorine gas in the gas phase in the presence of diluent gas. . The compound having a chlorine atom is chloromethane, chlorotrifluoromethane, chloropentafluoroethane, dichlorotetrafluoroethane, chlorotetrafluoroethane, chlorotrifluoroethane and chlorotree. Hexafluoroethane production method, characterized in that at least one compound selected from the group consisting of fluoroethylene. The method for producing hexafluoroethane according to claim 1 or 2, wherein the total amount of the compound having chlorine atoms contained in the gas mixture of step (1) is 1 vol% or less. The method for producing hexafluoroethane according to claim 1 or 2, wherein the total amount of the compound having chlorine atoms contained in the gas mixture of step (1) is 0.5% by volume or less. delete The method for producing hexafluoroethane according to claim 1 or 2, wherein the temperature during the reaction with hydrogen fluoride in the presence of the fluorination catalyst of step (1) is in the range of 150 to 480 ° C. The method for producing hexafluoroethane according to claim 1 or 2, wherein the molar ratio of hydrogen fluoride / organic material contained in the gas mixture of step (1) is in the range of 0.5-5. The method for producing hexafluoroethane according to claim 1 or 2, wherein the step of removing the acid content containing hydrogen chloride generated before step (2) is performed. The method of claim 1 or 2, wherein the step of separating chlorotetrafluoroethane and / or chlorotrifluoroethane and the separated chlorotetrafluoroethane and / or chlorotrifluoroethane are carried out before step (2). Hexafluoroethane production method characterized in that the step of restoring to step (1). The method for producing hexafluoroethane according to claim 1 or 2, wherein the total amount of the compound having chlorine atoms contained in the gas mixture of step (2) is 0.02% by volume or less. The method for producing hexafluoroethane according to claim 1 or 2, wherein the fluorinated compound contained in the gas mixture of step (2) mainly consists of hexafluoroethane. The diluent gas of step (2) is a gas containing one or more selected from the group consisting of tetrafluoromethane, hexafluoroethane, octafluoropropane and hydrogen fluoride. Hexafluoroethane production method, characterized in that. The method for producing hexafluoroethane according to claim 1 or 2, wherein the dilution gas of step (2) is a gas rich in hydrogen fluoride. The hexafluoroethane production according to claim 1 or 2, wherein the temperature of the reaction of the gas mixture containing the fluorinated compound of step (2) with the fluorine gas is in the range of 250 to 500 ° C. Way. The hexafluoroethane preparation according to claim 1 or 2, wherein the temperature of the gas mixture containing the fluorinated compound of step (2) and the fluorine gas is in the range of 350 to 450 ° C. Way. delete delete delete delete